1. Field of the Invention
This invention relates to radiation-hardenable diluents which are based on acrylic acid esters of alkoxylated 1,6-hexane diol; neopentyl glycol and tripropylene glycol each having a relatively low degree of alkoxylation for use in radiation-hardenable compositions which contain oligomers (also known as binders).
2. Description of the Prior Art
Radiation-hardenable compositions, particularly for coating applications are known in the art. In view of the restrictions on solvent content in the atmosphere, increasing efforts have been made to provide completely polymerizable systems which do not contain any volatile components, but instead consist of constituents which form either the whole or a part of the hardened film itself. Monomers which are useful for this purpose are known. For example, see U.S. Pat. Nos.:
3,594,410--Cohen et al--July 20, 1971 PA1 3,857,822--Frass--Dec. 31, 1974 PA1 4,058,443--Murata et al--Nov. 15, 1977 PA1 4,088,498--Faust--May 9, 1978 PA1 4,177,074--Proskow--Dec. 4, 1979 PA1 4,179,478--Rosenkranz et al--Dec. 18, 1979 PA1 4,180,474--Schuster et al--Dec. 25, 1979. PA1 E=Excellent--no removal of film PA1 G=Good--slight removal of film along etched lines PA1 F=Fair--removal of film on etched area PA1 P=Poor--removal of film. PA1 G=Good--no marking of film PA1 F=Fair--slight marking PA1 P=Poor--penetration and tearing of film. PA1 Paper--Opacity test panel form 013, from Morest Corp. PA1 Aluminum and tinplated steel panels from Q Panel Corp.
Among the diluents disclosed are polyacrylates of polyhydric alcohols such as polyethylene glycol, glycerol, neopentyl glycol, trimethylolpropane, pentaerythritol, etc., and polyacrylates of polyhydric alcohols reacted with alkylene oxide such as with ethylene oxide, i.e., addition products of one mole of trimethylol propane and 2.5 to 4 moles of ethylene oxide. However, it is pointed out in the context of U.S. Pat. No. 4,088,498 that compounds free from ether linkages are preferred.
The selection and proportion of useful diluents is very important. That is, the presence and proportion of these esters of acrylic acid as diluents in the radiation-hardenable composition influence the parameters of the system to be cured as well as the hardened film, for example, viscosity, cure rate, percent elongation, tensile strength, solvent resistance, scuff resistance and adhesion. For example, it is known that hexane diol diacrylate very effectively reduces viscosity of a resin, but at the same time has an extremely adverse effect upon properties of the oligomer. On the other hand, it is known that trimethylolpropane triacrylate has only a slight effect upon the properties of an oligomer, but is unable sufficiently to reduce the viscosity and at the same time imparts greater hardness but also poorer adhesion to the coating on account of the relatively high crosslinking density. Further, it has been found that certain diluents are irritating when handled. This, therefore, renders unacceptable certain diluents even though other properties are acceptable.